NM_000203.5:c.539G>C IDUA variant is a missense variant predicted to cause substitution of tryptophan by serine at amino acid 180 (p.Trp180Ser). This variant has been detected in at least four probands with MPS I. Of these individuals, three are compound heterozygous for the variant and another variant in IDUA that has been classified as pathogenic or likely pathogenic for MPS I by the ClinGen LD VCEP; all phase unconfirmed. The second variant was either c.46_57del (p.Ser16_Ala19del) (P by LD VCEP, Clinical Lab, 0.5 points), c.1861C>T (p.Arg621Ter) (LP by LD VCEP, Clinical Lab, 0.25 points), or c.1205G>A (p.Trp402Ter) (P by LD VCEP, PMID: 22976768, 25098213, possibly the same patient in both publications, 0.5 points). One individual is homozygous for the variant (Clinical Lab, 0.5 points). Total 1.75 points (PM3). At least one proband had reported deficiency of IDUA enzyme activity, and urinary dermatan and heparan sulfate elevation above normal range (PMID: 25098213; PMID: 22976768, Clinical Lab) (PP4). The highest population minor allele frequency in Genomes gnomAD v4.1.0 is 0.00001666 (1/60010 alleles) in the Admixed American population, which is lower than the ClinGen Lysosomal Diseases VCEP’s threshold for PM2_Supporting (<0.00025) (PM2_Supporting). The computational predictor REVEL gives a score of 0.959 which is above the threshold of 0.773, evidence that correlates with impact to IDUA function at the moderate level based on the specifications of the ClinGen Lysosomal Diseases VCEP (PMID: 36413997) (PP3_Moderate). There is a ClinVar entry for this variant (Variation ID:1021968). In summary, this variant meets the criteria to be classified as Likely Pathogenic for Mucopolysaccharidosis type I. IDUA-specific ACMG/AMP criteria met, based on the specifications of the ClinGen Lysosomal Diseases VCEP (Specifications Version 1.0.0.): PM3, PP3_moderate, PP4, PM2_Supporting. (Classification approved by the ClinGen Lysosomal Diseases Variant Curation Expert Panel on May 7, 2025)